The present invention relates to a particle counting apparatus for obtaining a total counting value of particles contained in a liquid sample or a density of the particles in the liquid sample, that is, a concentration of the sample by detecting a number of the particles contained in the sample which flows in a flow cell.
The light active particle counting apparatus for counting particles in the sample by irradiating a light beam or a laser beam to the particles and detecting a pulse-wise scattering light, fluorescence or sound wave from the particles in the sample which flows in a tube is widely known.
For example, Japanese Patent Laid-open Nos. 50-11290(1975) and 63-142234(1988) disclose particle counting apparatuses for counting the particles by irradiating the laser beam to the particles and detecting the scattering light from the particles.
Further, Japanese Patent Laid-open Nos. 50-68174(1975) (corresponding to U.S. Pat. No. 4,009,443) and 50-120880(1975) (corresponding to U.S. Pat. No. 3,864,551), and Review of The Scientific Instruments, Vol. 43(1972), pp 1407-1412, disclose correcting methods of a particle counting error which arises when plural particles are simultaneously passed through a detection light beam. However, as such correcting methods are performed based on an estimation of the error by detecting a uniform flow of the sample, it is difficult to expect an accurate particle counting.
Japanese Patent Laid-open No. 2-162234(1990) discloses a particle counting method which counts not only a uniform density portion of the sample flow, but also a top end and last end of the sample flow by dividing the sample flow with time and detecting particles in the divided flows. However, such reference does not show how to correct for saturation of the counting value when plural particles irradiated with a light beam so as to be counted are overlapped in the light beam. Accordingly, there is a problem relating to an accurate estimation of the particle counting in the end portions of the sample flow.